The present invention relates to a block copolymer having excellent solvent resistance, as well as desirable processability and more particularly the present invention relates to a block copolymer composed of alkylperfluoroalkylethylenesiloxy blocks and diphenylsiloxy blocks which block copolymer has desirable processability properties and excellent solvent resistance.
Dimethylpolysiloxane polymers which are cured with peroxide curing catalysts to produce heat vulcanizable silicone rubber elastomers are well known in the art. Such heat vulcanizable elastomers have the desired low and high temperature stability that is well known of silicone elastomers. However, one difficulty in the production of such elastomers is that the diorganopolysiloxane gums that are utilized have viscosities of 1,000,000 to 200,000,000 centipoise at 25.degree. C. Such materials with the incorporation of the necessary amounts of filler in them tend to be very viscous, as can be appreciated, and very tacky. Accordingly, such polymers are very difficult to process because of their tackiness on standard processing equipment in the preparation of such compositions prior to curing them at elevated temperatures.
There have been many attempts to alleviate the processing problems in the treating of such uncured heat vulcanizable silicone rubber compositions. One approach to the problem is to utilize process aids. Another approach is that disclosed in the foregoing Bostick, U.S. Pat. No. 3,337,497 which is to form a block copolymer having diphenylsiloxy blocks in the copolymer along with dimethylsiloxy blocks. The advantages of having such diphenylsiloxy blocks is that such blocks depending on the number of siloxy units in the block are crystalline at temperatures up to 200.degree. C. and above. Accordingly, they impart to the diorganopolysiloxane block copolymer a certain amount of stiffness which prevents the polymer from being tacky and accordingly facilitates the processing of heat vulcanizable silicone rubber compositions in the uncured state. However, such polymers while being processable in the uncured state do not have as high a solvent resistance in hydrocarbon fluids as would be desired.
Solvent resistant heat vulcanizable silicone rubber compositions having fluorinated substituent groups in the polymer are well known-- see, for instance, U.S. Pat. No. 2,979,519 of Pierce et al and U.S. Pat. No. 3,179,619 of Brown.
However, one disadvantage of such polymers which are utilized to produce heat vulcanizable silicone rubber compositions, such as that disclosed in the above patents, is that the fluorinated gums are even more tacky than dimethylpolysiloxane gums and thus are extremely difficult to process even at temperatures below room temperature. To alleviate this problem, certain process aids have been developed for fluorosilicone polymers. However, these process aids have not completely alleviated the problem. Further, the Bostick, U.S. Pat. No. 3,337,497, specifically discloses that this block copolymer be free of halogen hydrocarbon substituent groups. Accordingly, little, if any, attempt has been made up to the present time to produce such block copolymers with fluorinated substituent groups.
It is one object of the present invention to produce a solvent resistant block copolymer having desirable processability properties in the uncured state.
It is another object of the present invention to provide a solvent resistant block copolymer composed of diphenylsiloxy blocks and alkylperfluoroalkylethylenesiloxy blocks.
It is an additional object of the present invention to provide an economical process for producing solvent resistant block copolymers with excellent processability properties wherein the block copolymer is composed of diphenylsiloxy blocks and alkylperfluoroalkylethylenesiloxy blocks.
It is yet an additional object of the present invention to provide a process for producing high yields of a solvent resistant block copolymer having desirable processability properties.
It is still an additional object of the present invention to provide a heat vulcanizable silicone rubber composition having as the main polymer a block copolymer composed of diphenylsiloxy blocks and alkylperfluoroalkylethylenesiloxy blocks wherein the cured elastomer that is formed from the composition has excellent solvent resistance.
These and other objects of the present invention are satisfied by means of the disclosure set forth herein below.